Known bag tubes have a film material of plastic which forms an end-face wall and two side walls of the tube, wherein the side walls are welded (or connected in another manner) to one another along two side sections, and a shoulder piece which comprises a closable outlet piece and a flange fastened on the end-face wall, preferably curved just as the end-face wall.
The invention relates to a method for manufacturing bag tubes, wherein a web of film material is folded about a fold line running in its longitudinal direction. The sections of the web are laid on one another, along strips which are arranged at distances from one another and which run transversely to the fold line, and are connected to one another in order to form a row of pockets. A hole is cut in each pocket in the region of the fold line and then a shoulder piece is introduced into each pocket. The shoulder piece comprises a closable outlet piece and a flange projecting from the piece. The outlet piece of the shoulder piece is inserted through the hole, the flange of the shoulder piece is connected to the film material, the outlet piece of the shoulder piece is closed, the pocket then from the open end is filled, and finally the open end is closed.
In known methods of this type it is difficult to cut a round hole precisely into the film material forming the end-face wall and to prevent a distortion of the film material which may lead to shoulder pieces seated too obliquely in the bag tubes.
The object of the invention lies in avoiding these difficulties, thus to permit a precise cutting of the hole and avoiding a distortion of the film material.
According to the invention this object is achieved in that, for cutting the hole into each pocket, the film material of the pocket in the region of the fold line is shaped and clamped between two shaping parts and then in one of the shaping parts a knife is displaced and moved to a counter knife on the other shaping part.
The applied shaping parts may usefully be curved, roughly about an axis perpendicular to the connection plane of the two strips limiting the pocket. In the same manner the flange of the shoulder piece to be inserted may also be curved.
The pocket may in the axial direction be relatively long. So that the two shaping parts, of which one must be introduced into the pocket, may cooperate precisely despite this, the knife and the other shaping part may usefully comprise a centering pin and a receiving bore.